The evidence of radiation effects in embryos and fetuses exposed to Chernobyl fallout and the question of dose response.

Current legal frameworks for radiation exposure limits are based on the risk models of the International Commission on Radiological Protection (ICRP). In Publication 90 (2003), ICRP presents a safe (threshold) dose range of up to 100 mSv for radiogenic effects resulting from in utero exposure and bases this conclusion on the findings in Hiroshima and Nagasaki. However, a variety of observations of congenital malformations, fetal loss, stillbirths and infant deaths, as well as of Down's syndrome and other health defects in children after the Chernobyl accident exposures suggest that the A-bomb survivor data are incomplete. The Chernobyl findings are generally marginalized or even denied because of the low values of the estimated human exposures and the inconsistency of the results with the accepted risk models. One explanation for the observations is that physical dosimetric models have underestimated the effective exposure. This possibility is supported by biological dosimetry in the contaminated regions. The assumptions about effects after in utero exposure by incorporated radionuclides need to be revised.